Most elegant way to log when early return (quite common when defensive programming)?

When doing defensive programming, I often have some early-return code. In addition, I need to write some log warning that the function returns because of what problem.

void f(A a) {
  var b = a.b;
  if (b == null) {
    Log.warn('f skip running since b==null');
    return;
  }

  var c = some_func(b);
  if (c == null) {
    Log.warn('f skip running since c==null');
    return;
  }

  another_func(c);
}

I know I can use null-aware operators like ?. but it cannot print warnings when it is null.

I have also tried another approach:

void f(A a) {
  var errorMessage = fCore(a);
  if (errorMessage!=null) Log.warn(errorMessage);
}

String fCore(A a) {
  var b = a.b;
  if (b == null) {
    return 'f skip running since b==null';
  }

  var c = some_func(b);
  if (c == null) {
    return 'f skip running since c==null';
  }

  another_func(c);
  return null
}

But that is also kind of verbose.

Is there a better approach? Thanks!

EDIT

I call it like:

void outer_func() {
  one_func();
  f(); // even if f skip running, I want two_func still run, etc
  two_func();
  ...
}

Thus, I cannot simply do something like throw LogWarnException('...') and catch at outermost function.